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Thread: "Figure 4" installation vs. Y-plan

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    Default "Figure 4" installation vs. Y-plan

    Hi,

    Please forgive my lack of knowledge here! I have an Evohome retrofitted to my Y-plan system, however am now looking a changing a few things around and I read through these forums the "figure 4" installation is considered optimum - that is the heating circuit always on (though flow restricted by every radiator having a Evohome valve with a single 2-way valve, thus definitely requires a bypass valve) and relay to introduce HW on demand.

    My question is WHY is this optimal? Perhaps naively I would've thought the Y-plan setup with the 3-way value would be better as at any given time the system can provide heating OR hot water OR heating and hot water.

    The only obvious advantage I can see is within the Evohome software: for whatever reason when setting up as Y-plan the configuration options to set boiler cycle and run times are not available, this despite the fact the Evohome still has exclusive control over the boiler (even in setups like mine which incorporate pump overrun it still has exclusive control over demand).. I don't see why this 'logic' / 'limits' cannot be used for Y-plan setups (eg. don't cycle boiler more than x times an hour and don't run boiler for less than x minutes)?

    Quite possibly missing something - maybe on both on the optimal pipework/valve setup AND a good reason why the above can't be configured for Y-plan - look forward to being educated!

    Thanks.
    Last edited by SimonW500; 1st March 2015 at 06:22 PM.

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    Quote Originally Posted by SimonW500 View Post

    The only obvious advantage I can see is within the Evohome software: for whatever reason when setting up as Y-plan the configuration options to set boiler cycle and run times are not available, this despite the fact the Evohome still has exclusive control over the boiler (even in setups like mine which incorporate pump overrun it still has exclusive control over demand).. I don't see why this 'logic' / 'limits' cannot be used for Y-plan setups (eg. don't cycle boiler more than x times an hour and don't run boiler for less than x minutes)?

    Quite possibly missing something - maybe on both on the optimal pipework/valve setup AND a good reason why the above can't be configured for Y-plan - look forward to being educated!

    Thanks.
    For the reason you identified Fig 4 is optimal for new installations. Modern high efficiency boilers may benefit from adjusting the cycle rate, particularlupy oil boilers. It also means that the hot water zone valve is only powered when hot water is required, meaning it will last longer.
    It's basically less parts so inherently easier to install.

    Hope this makes sense?
    I work for Resideo, posts are personal and my own views.

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    Quote Originally Posted by top brake View Post
    For the reason you identified Fig 4 is optimal for new installations. Modern high efficiency boilers may benefit from adjusting the cycle rate, particularlupy oil boilers. It also means that the hot water zone valve is only powered when hot water is required, meaning it will last longer.
    It's basically less parts so inherently easier to install.

    Hope this makes sense?
    For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

    Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

    (thanks in advance)

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    Quote Originally Posted by SimonW500 View Post
    For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

    Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

    (thanks in advance)
    I don't see why the options couldn't be provided for either S-plan or Y-plan. I think the issue is that the EVOHOME controller likes to separate "boiler control" from "heat" or "water" controls. So if you have a set-up where there is only a single relay that basically is there to cycle the boiler regardless of whether it is heat or water, then you get these options. But in the event of multiple BDR91s, these options are gone. It is a limitation of the programming but it could be enhanced.

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    Quote Originally Posted by SimonW500 View Post
    For new installations I can fully follow the less parts / simpler design logic. Yet for existing installations, I still cannot understand the benefit of rejigging a working Y-plan system (perhaps the answer is there isn't one?).

    Also re. setting boiler cycle and minimum runtime settings I still cannot see why this couldn't be configured for a Y-plan (other than the software currently doesn't allow it) - am I missing something?

    (thanks in advance)
    Quote Originally Posted by jonstatt View Post
    I don't see why the options couldn't be provided for either S-plan or Y-plan. I think the issue is that the EVOHOME controller likes to separate "boiler control" from "heat" or "water" controls. So if you have a set-up where there is only a single relay that basically is there to cycle the boiler regardless of whether it is heat or water, then you get these options. But in the event of multiple BDR91s, these options are gone. It is a limitation of the programming but it could be enhanced.
    without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

    if this level of control is required you need to install as Fig 4
    I work for Resideo, posts are personal and my own views.

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    Quote Originally Posted by top brake View Post
    without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

    if this level of control is required you need to install as Fig 4
    That's how it is today....but Honeywell "could" enhance this through a firmware update to offer these options for s-plan and y-plan configurations as well.

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    Quote Originally Posted by top brake View Post
    without a BOILER RELAY you do not have control over the cycle rate and minimum runtime

    if this level of control is required you need to install as Fig 4
    Seems Jon and myself are angling at the same question!

    Following a Y-plan installation, requiring 2 wireless relays to fully control both sides, the Evohome still has full and exclusive control over boiler demand and therefore COULD control cycle rate and minimum runtime. My question is therefore validating my understanding / trying to understand WHY this currently isn't an option (a decision made on a Friday afternoon perhaps?!).

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    Quote Originally Posted by SimonW500 View Post
    Seems Jon and myself are angling at the same question!

    Following a Y-plan installation, requiring 2 wireless relays to fully control both sides, the Evohome still has full and exclusive control over boiler demand and therefore COULD control cycle rate and minimum runtime. My question is therefore validating my understanding / trying to understand WHY this currently isn't an option (a decision made on a Friday afternoon perhaps?!).
    If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
    Sensible Heat
    SensibleHeat.co.uk

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    Quote Originally Posted by SensibleHeatUK View Post
    If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
    Yes I figured as much - thanks for the confirmation - indeed a route I may go down.

    However, this is more a 'fudge' to work within the artificial software limitations of the current Evohome options right? As Jon and myself state these options could (in theory) be simply updated to work as-is?

    Further, are you able to comment on my original question re. efficiencies of figure 4. vs. Y-plan? If I am moving things around with my wiring I might as well consider moving the plumbing arrangement around as well.. if of course there is a benefit?

    Thanks!

    (nb. equally happy to be wrong.. I'm just trying to further my understanding as opposed to hammer home a point/agenda!

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    Quote Originally Posted by SensibleHeatUK View Post
    If you add a third BDR to your S or Y-plan setup, registered to Evo as a Boiler Controller (re-wiring the boiler demand signals appropriately), then you can have control over the boiler too. It is simply that most installations are not set up this way, either for cost reasons (although an extra BDR is not a massive cost increase in relatively terms), or because the system has been installed with as little disruption to the existing wiring as possible.
    But as I have found out, if you install this way with three BDRs, then neither zone valve BDR is necessarily operated at the same time as the Boiler Demand BDR. So if you did this on an S-plan, the boiler demand could effectively be calling heat and pumping straight through an automatic bypass. On a y-plan it is less of an issue, as the valve will be held in the last port of call. Evo is not designed to work in this way according to Top Brake; see this post here: http://www.automatedhome.co.uk/vbull...ll=1#post21263

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